Conventional exhaust gas recirculation apparatuses are made in such a way that they connect the exhaust pipe and intake port by external piping and open a normally closed EGR valve provided in the path of said external piping using vacuum pressure within the intake port during the intake stroke, thereby causing exhaust gas to recirculate through the above-noted external piping.
However, it turns out that always taking exhaust gas into the combustion chamber on the intake stroke causes lean combustion in conventional exhaust gas recirculation apparatuses as described above, and even though a satisfactory combustion situation can be obtained without difficulty in the light-load operating range in which there is naturally an excess of air, there are problems in that, in the high-load operating range in which the proportion of air with respect to fuel is low, combustion conditions are not good and black smoke with large amounts of soot is readily generated.
Further, because it becomes necessary that the external piping be provided with an EGR valve, the installation space required for the engine increases in volume, and moreover, there is a problem in that careful consideration must be given to providing heat-insulating measures for the external piping which will reach high temperatures as a result of the flow of exhaust gas and to constraints in terms of layout.
In addition, there are also problems in engines equipped with turbochargers, etc., in that exhaust gas cannot be recirculated satisfactorily in operating ranges in which the boost pressure (supercharging pressure within the intake pipe) is higher than the exhaust pressure.
This invention takes these actual circumstances described above in consideration and makes its objective to provide an exhaust gas recirculation apparatus that can recirculate exhaust gas into the combustion chamber only in required operating ranges, and moreover, can recirculate exhaust gas into the combustion chamber without using external piping, and further, in engines equipped with turbochargers, etc., can recirculate exhaust gas acceptably even in operating ranges in which the boost pressure is higher than the exhaust pressure.